1. Field of the Invention
The present invention relates to the field of mesoporous silica materials useful for separations. More particularly, it relates to a mesoporous silica having grafted therewith an ionic liquid that is particularly useful for certain separations.
2. Background of the Art
Mesoporous materials have been known to researchers for many years, and are used for a variety of applications. In general these materials are inorganic, solid materials characterized by a structure which comprises pores, the pores having average diameters in a general range of from 2 to 50 nanometers (nm). These pores may be uniform with constant diameters, or non-uniform with a variety of diameters. The porous structure provides for a large internal surface area with adsorptive capacity for molecular species which are capable of entering the pores. The pores may penetrate essentially the entire volume of the solid material, and therefore may be essentially two-dimensional or three-dimensional (i.e., channels), depending upon the configuration of the material's structure as a whole.
Mesoporous materials may be amorphous or crystalline. Examples of mesoporous materials include synthetic or natural crystalline pure silicates and aluminosilicates. Such may also be referred to as “framework aluminosilicates,” where the framework is based on a three-dimensional network of [(Al,Si)4] tetrahedra which are linked to each other, at the corners, by shared oxygen atoms. Substitution of aluminum for silicon generates a charge imbalance, requiring the inclusion of an additional cation.
Mesoporous silicas have been shown to be able to successfully support ionic liquid catalysts including an acetate counterion, such as is shown in China Publication No. CN 101773852 (14 Jul. 2010). That publication describes functionalizing the surface of the mesoporous silica, followed by reaction with an imidazolium species. The catalyst thus prepared is used for preparing vinyl acetate in an acetylene method.
However, despite successful application of such mesoporous, or potentially mesoporous, silica materials in certain applications, some of these materials suffer from less than desirable performance with respect to dispersion in a given medium; resistance to diffusion; selectivity in separations operations; contact with adsorbates and/or reactants; and/or other difficulties in their use in specific industrial streams. In view of the above it is desirable to develop new silica-based mesoporous materials to reduce or eliminate one or more of these problems.